Generally, a washing machine (e.g., a fully automatic washing machine) includes a tub which stores water (washing water or rinsing water), a washing tub which is rotatably installed inside the tub and accommodates laundry, a pulsator which is rotatably installed inside the washing tub and generates a water stream, and a motor which generates a driving force for rotating the washing tub and the pulsator, and serves to remove contaminants of the laundry using surface activity of a detergent and the water stream.
The washing machine performs a washing operation through a series of processes including a washing process which separates the contaminants of the laundry with the water (specifically, the washing water) containing the dissolved detergent, a rinsing process which rinses bubbles or remaining detergent of the laundry with the water (specifically, the rinsing water) not containing the detergent, and a spin-drying process which removes the water contained in the laundry by high speed rotation. When the washing operation is performed through the series of processes, the motor is driven with a target RPM and operation ratio in each of the washing process, the rinsing process and the spin-drying process.
The motor RPM and operation ratio in each process is set according to a weight (a load) of the laundry, and the motor is rotated at a speed determined by the set RPM and operation ratio. Therefore, recently, a study on a method of detecting the weight of the laundry is being carried out to optimize a water level and the washing process before the main process.